A Variety of methods and techniques have been developed for simulating the appearance of sunlight on world globe models. In most embodiments of this concept, a globe model representing the earth is internally illuminated by a baffled light source. The globe is typically semi-transparent, and the baffle is arranged so that one half of the globe is in simulated sunlight, while the remaining half is in simulated darkness. Manual or automatic mechanisms are employed to rotate the globe and baffle with respect to one another so that the demarkation between the night and day hemispheres of the globe rotate once each day (typically one revolution every 23 hours, 56 minutes and four seconds to simulate sidereal time).
The prior art mechanisms for simulating this day/night demarkation range from simple to complex, from manual to automatic. One of the earliest prior art devices is described by Schulse in U.S. Pat. No. 1,959,601 issued on May 22, 1934. Schulse describes a globe which rotates once each 24 hours. A lamp is fixed within and with respect to the globe behind a shield/filter to produce the desired day/night effect. The filter itself rotates about the lamp on an axis which is displaced 23.5 degrees with respect to the polar axis of the globe once each 365 days to simulate the effect of the seasons on the day/night illumination pattern. A conventional clock automatically drives the globe and shield/filter. Schulse's mechanism is relatively complex involving multiple gear trains and slip clutches, worm drives and concentric, rotating shafts all of which contribute to a relatively expensive chronological instrument. Devices such as this have not been accepted into the marketplace.
Others, such as Carlson in U.S. Pat. No. 4,936,779 have provided an internally illuminating globe which simulates the day/night pattern on the surface on the earth with a substantially less complex mechanism. In Carlson, a lamp and interior baffle rotate once every 24 hours with respect to the globe to simulate a day/night illumination pattern through a semi-transparent globe shell. As is well known, the actual day/night pattern of the surface of the earth oscillates through .+-.23.5 degrees with respect to the polar axis as the earth completes a circumrevolution about the sun. In order to avoid the complexities of devices such as those described by Schulse, Carlson employs an adjustable cam mechanism by way of an exterior knob and flexible cable. Adjustment of the knob rocks the baffle back and forth about an axis passing through the equator of the model to simulate the seasonal variation of the light pattern on the globe. Although Carlson's mechanism is substantially less complex than many prior art devices, the device is believed to nevertheless remain excessively complex to succeed in the marketplace.
Whereas Carlson's and Schulse's devices described above are completely automatic (i.e. motor driven) others have attempted to avoid complexity by combining a completely manually driven globe simulating the day/night illumination pattern on the earth. The device disclosed by Gardin in U.S. Pat. No. 3,305,946 is intermediate in complexity between Schulse and Carlson in that adjustment of a single time of day ring, and day of year ring is sufficient to position an internal lamp with baffle appropriately to simulate the correct day/night pattern on the surface of the globe for a given time of day and year. Nevertheless, Gardin's mechanism still employs a plurality of beveled gears, counter-rotating shafts, etc. and has not found commercial acceptance in the marketplace. Other examples of day/night illuminating globes are provided by Veazey in U.S. Pat. No. 4,102,121, Domen in U.S. Pat. No. 4,714,351 and Mariotti in U.S. Pat. No. 3,197,893. In each of the devices described in these patents, a different mechanism is employed to impart an appropriate "nodding" motion to an internal baffle to simulate the effect of the earth's orbit about the sun on a simulated day/night pattern for their globes. In each case, the mechanisms are complex and do not lend themselves to inexpensive production techniques.
Therefore, a need exists for a world globe model which indicates a day/night demarkation on the surface of the globe model with a simple, reliable and inexpensive mechanism.
A need also exists for a globe model which simulates a day/night illumination pattern with a simple, reliable and economical mechanism.